1. Field of Invention
The present invention relates to power device protection circuits, and more particularly to smart power devices.
2. Description of Related Art
Modern electronic devices need power devices to provide and transform electric power. There is a vast array of power devices at present. Most of these power devices support large currents, which in turn can be hazardous for the power devices themselves. For example, the current causing a temperature to exceed a maximum allowed temperature, or a current to exceed a maximum current can be detrimental for the power device, including causing the burnout of the device. Therefore, in modern circuits the power devices are typically protected against overheating and over-current faults, and other hazardous operating condition.
Existing designs limit the main device current, but they may not shut down the power device. However, in some circumstances, shutting down the power device is the most sensible response to the fault.
In some protected power devices a temperature independent voltage is used to analyze and control the operating characteristics of the power device, such as its temperature. However, the temperature independent voltage is often provided by a circuit on the protected chip, which takes numerous complex mask steps to create.
Other existing designs use additional auxiliary lines, e.g. “flag lines”. Using flag lines increases the number of pins, and requires the processing of additional data. Furthermore, often flag lines in discrete power devices generate too small current signals because they utilize parasitic bipolar junction transistors with an amplification factor beta as low as two. Since control circuits are coupled to the flag lines, bigger signals and more current are needed. Also, sensitivity to smaller changes in the control line current would be desirable for more precise, “smart” power management.
Furthermore, often all flag lines are tied in parallel or “wired ored.” In such designs it can not be determined, which power transistor had the fault.
For at least the above reasons, developing protected smart power devices is a high priority.